I spent more time playing this than I should have, it was fun.
Few thing I can suggest. Make Ai more aggressive, or have different Ai types with different level of aggression and aim level. Make pistol projectiles live longer or faster, when I shoot someone and he shoots back we both move in opposite direction and bullets never catch us.
Few bugs I saw. Weapon spawned in solid circle making it inaccessible. UI elements of phone for fire and movement remained on screen after the end of level.